Preamplifier integrated circuit on flex circuit for magnetic media storing devices

ABSTRACT

A preamplifier integrated circuit (IC) for a magnetic storage device comprises a plurality of channels, each including at least one preamplifier and a plurality of groups. Each of the groups includes at least one of the channels. A passivation layer is arranged adjacent to at least one interconnecting layer. A plurality of first external connections external to the IC are arranged in openings in the passivation layer, are in contact with at least one of the interconnecting layers, that distribute a first potential to the at least one preamplifier of the plurality of channels, and communicate with the plurality of groups. Each of the plurality of first external connections distributes the first potential to first respective ones of the plurality of groups independently of others of the plurality of groups.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 10/319,391, filed Dec. 12, 2002. The disclosure of the above application is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to devices for reading and writing on magnetic recording media, and more particularly to a preamplifier integrated circuit and a flex circuit for reading and/or writing channels of a magnetic storage device.

BACKGROUND OF THE INVENTION

Conventional magnetic storing devices such as disk drives read information from and write information to a magnetic storage medium. The disk drive typically includes a moveable arm that is positioned relative to the magnetic storage medium by a high speed linear motor or another positioning device. The arm is usually associated with multiple read and/or write channels.

Information is written to the magnetic storage medium using a write channel and a write circuit. Each write channel and circuit is capable of inducing a magnetic field with a first or second polarity adjacent to the magnetic storage medium, which stores the magnetic field. One polarity represents one digital value (such as a “1”). The opposite polarity represents the other digital value (such as a “0”). Information is read from the magnetic storage medium using a read channel and read circuit. Each read channel and circuit is capable of sensing the magnetic field stored on the magnetic storage medium.

Referring now to FIG. 1, an single-layer flexible substrate or flex circuit 10 is mounted on or otherwise connected to an arm (not shown) of a disk drive (not shown). The flex circuit 10 can be a flexible substrate as shown. While a specific outer shape of the flex circuit 10 is shown, the shape of the flex circuit 10 will vary according to the specific application.

A connector 14 can be mounted on or otherwise connected to the flex circuit 10. The connector 14 typically provides a first mating plug for receiving a second mating plug (both not shown). The second mating plug may be connected by conductors or wires to a read channel of the disk drive. A preamplifier IC 18 is also mounted on or otherwise connected to the flex circuit 10. Inductive elements 20 such as inductive coils or other devices are generally located near one end of the flex circuit 10. Typically, one or more inductive elements 20 are associated with each read and/or write channel.

The flex circuit 10 includes traces that are generally identified at 22. The traces 22 provide connections from the connector 14 to the preamplifier IC 18. Likewise, the flex circuit 10 includes traces that are generally identified at 24 (only one shown). The traces 24 provide connections from the preamplifier chip 18 to the inductive elements 20.

Referring now to FIG. 2, the flex circuit 10 typically includes a flexible substrate 30 and a patterned conductive layer 34 formed on the substrate 30 that defines the traces 22 and 24. The traces 22 and 24 relay read and/or write inputs/outputs (I/O), power and ground to and from the connector 14, the preamplifier IC 18 and/or the inductive elements 20. An insulating layer 38 may also be formed on an outer surface of the patterned conductive layer 34 to insulate the traces 22 and 24. While a single patterned conductive layer 34 is shown, multiple patterned conductive layers 34 may be provided. If multiple patterned conductive layers 34 are provided, they can optionally be interconnected by vias. While the flex circuit 10 is shown, other circuits such as printed circuit boards (PCBs) can be used.

The preamplifier IC 18 is typically formed on a wafer using photolithography. Film deposition, masking, etching and doping steps are repeated several times until all of the active devices of the preamplifier IC have been formed. Then, the individual devices in each preamplifier IC are interconnected using one or more metal layers, which are separated by insulating layers. Vias provide interconnections between the separated metal layers. After the last metal layer has been patterned, a passivation layer is deposited to protect the IC from damage and/or contamination. Openings are etched in the passivation layer of the preamplifier chip 18 to allow electrical contact to be made with the metal layers using solder bumps and traces on the flex circuit 10.

The preamplifier circuit 18 typically includes multiple read and/or write channels and requires connections to read and/or write I/O, one or more power sources, and ground. Typically, the power supply voltages are delivered to the preamplifier IC 18 using a trace and a solder bump. After reaching the IC, power distribution is performed in the metal layers of the IC. Ground and the other power supply signals are also distributed in the metal layers of the IC in a similar manner.

As the number of read and write channels increases, the number of interconnections that must be patterned in the metal layers of the IC also increases. As the number of interconnections increases, the complexity of the metal interconnection layers that are used for power and ground also increases. The increased complexity and/or additional metal layers further increase the cost of fabricating the preamplifier IC. Since power distribution is performed in the metal layers of the IC, relatively high currents and voltages must be carried by sub-micron traces in the metal layers of the IC and by the solder bumps. I²R heating in the metal layers will also increase die temperatures during operation.

SUMMARY OF THE INVENTION

A preamplifier integrated circuit (IC) for a magnetic storage device includes a plurality of channels, each including at least one preamplifier and one or more interconnecting layers. A passivation layer is arranged adjacent to the interconnecting layers. A plurality of first external connections are arranged in openings in the passivation layer, are in contact with at least one of the interconnecting layers and are adapted to distribute a first potential to the preamplifiers. The plurality of channels are arranged in a plurality of groups, each of the plurality of groups includes at least one of the channels. At least one of the first external connections independently communicates with at least a respective one of the plurality of channels. The first potential is distributed to a respective one of the plurality of groups via the corresponding at least one of the external connections.

In other features of the invention, second external connections are arranged in the openings in the passivation layer, contact at least one of the interconnecting layers and are adapted to distribute a reference potential to the preamplifiers. At least one of the second external connections independently communicates with at least the respective one of the plurality of channels. The reference potential is distributed to the respective one of the plurality of groups via the corresponding at least one of the external connections.

In other features, the first external connections are arranged one of radially inside and radially outside of the second external connections. Second traces are arranged on an outer surface of the passivation layer. The second external connections are connected together using the second traces.

In still other features, third external connections are arranged in the openings in the passivation layer, contact at least one of the interconnecting layers and are adapted to distribute a second potential to the preamplifiers. At least one of the third external connections independently communicates with at least the respective one of the plurality of channels. The second potential is distributed to the respective one of the plurality of groups via the corresponding at least one of the third external connections.

In still other features, the first external connections can be connected together using a first trace. The third external connections can be connected together using a third trace that does not overlap the first trace.

In other features, ground shield external connections can be connected using a ground shield trace. Second external connections are arranged in openings in the passivation layer, contact at least one of the interconnecting layers and are adapted to independently distribute the reference potential to the groups. A second trace is arranged on an outer surface of the passivation layer. The second external connections are connected together using the second trace. The first and third traces are arranged between the ground shield trace and the second trace. The second trace on the passivation layer connects the ground shield external connections to the second external connections.

In still other features, an insulating layer is arranged adjacent to the second trace. Fourth external connections are arranged on the passivation layer that are associated with at least one of read and write inputs/outputs. A first group of traces arranged on the passivation layer that connect the fourth external connections to the preamplifiers. The preamplifiers include at least one of a read preamplifier and a write preamplifier.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 illustrates a connector and a preamplifier (PA) integrated circuit (IC) mounted on a flex circuit according to the prior art;

FIG. 2 is a cross-sectional view of the flex circuit according to the prior art; and

FIG. 3 is a bottom plan view illustrating solder bumps and the passivation layer of the preamplifier IC according to the present invention;

FIG. 4 illustrates the preamplifier IC of FIG. 3 and traces and a ground plane of a flex circuit according to the present invention; and

FIG. 5 illustrates a side cross-sectional view of the preamplifier IC.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements.

Referring now to FIG. 3, a bottom plan view of a preamplifier IC 40 according to the present invention is shown. The preamplifier IC 40 includes a plurality of channels that include read and/or write channels. Each channel is associated with one or more conventional preamplifier circuits as is known in the art. Connections are made to the preamplifier IC 40 using solder bumps that are connected to one or more of the metal layers of the preamplifier IC 40 through openings etched in a passivation layer 41 of the preamplifier IC 40.

For example, in the exemplary embodiment, the preamplifier IC 40 includes eight write channels w₀, w₁, w₂, w₃, w₄, w₅, w₆, and w₇ and eight read channels r₀, r₁, r₂, r₃, r₄, r₅, r₆, and r₇. Write and read channels w₀, r₀, r₁ and w₁ are located (from bottom to top) along a first edge 42. Write and read channels W₂, r₂, w₃, r₃, w₄, r₄, r₅, and w₅ are located (from right to left) along a second edge 44. Write and read channels w₆, r₆, r₇ and w₇ are located (from top to bottom) along a third edge 46. Read/write I/O solder bumps 48-1, 48-2, . . . , and 48-n (collectively identified as 48) are located along a fourth edge 47. In the exemplary embodiment in FIG. 3, the read/write I/O solder bumps 48 are associated with WDY, WDX, LB, RDY, RDX, SDATA, SCLK, SDEN, ABHV, FLT, and WRN inputs and outputs.

The write and read channels are preferably arranged on opposite sides of corners 49-1 and 49-2 of the preamplifier circuit 18 to reduce the number of solder bumps, as will be described below. For example, write channels w₁ and w₂ are located adjacent to each other in one corner 49-2. Write channels w₅ and w₆ are located adjacent to each other in another corner 49-1. As can be appreciated, the relative positions of the read channels, write channels, power supplies, ground, and read/write I/O can be altered from that shown in FIGS. 3 and 4 without departing from the scope of the present invention.

First solder bumps 50-1, 50-2, . . . and 50-m (generally identified by reference number 50) are formed in openings in the passivation layer 41 and are used to distribute a first voltage level V_(EE) to the preamplifier IC 40. While solder bumps are disclosed, any external connection may be used. The first solder bumps 50 are preferably formed in a “U”-shape or ring. Additional solder bumps 52-1, 52-2, and 52-3 are used to bring the first voltage source onto the preamplifier IC 40 and to terminate the circuit. Preferably, and the first solder bumps 50 are located closest to corresponding write channels. For example, solder bump 50-1 is located closest to w₇ and solder bump 50-2 is located closest to w₆ and w₅.

Second solder bumps 54-1, 54-2, . . . and 54-q (generally identified by reference number 54) are formed in openings in passivation layer 41 and are used to distribute a second voltage level V_(DD) to the preamplifier IC 40. The second solder bumps 54 are preferably formed in a “U” shape or ring inside or outside of the first solder bumps 50. Additional solder bumps 56-1, 56-2, and 56-3 are used to bring the second voltage source V_(DD) onto the preamplifier IC 40 and to terminate the circuit.

Third solder bumps 58-1, 58-2, . . . and 58-p (generally identified by reference number 58) are formed in the openings in passivation layer 41 and are used to distribute ground to the preamplifier IC 40. The third solder bumps 58 are preferably formed in a “U” shape or ring inside of the first and second solder bumps 50 and 54, respectively. Additional solder bumps 60-1 and 60-2 are used to bring ground on-chip. The solder bumps 52, 56 and 60 may be formed on top of the passivation layer 41 and/or in openings etched into the passivation layer 41.

Each channel includes a read channel and/or a write channel. A group includes one or more channels. One or more solder bumps 54 are used to connect V_(DD) to each group. One or more solder bumps 50 are used to connect V_(EE) to each group. One or more solder bumps 58 are used to connect ground to each group. For example in FIGS. 3 and 4, there are six groups. Two of the groups are associated with two read/write channels. Specifically, V_(DD) 54-1 and V_(EE) 50-1 are associated with w₇ and r₇. V_(DD) 54-2 and V_(EE) 50-2 are associated with w₆, r₆, w₅, and r₅. V_(DD) 54-3 and V_(EE) 50-3 are associated with w₄ and r₄. V_(DD) 54-4 and V_(EE) 50-4 are associated with w₃ and r₃. V_(DD) 54-5 and V_(EE) 50-5 are associated with w₂, r₂, w₁, and r₁. V_(DD) 54-6 and V_(EE) 50-6 are associated with w₀ and r₀.

A conducting layer is formed on the passivation layer 41. This conducting layer connects the solder bumps 58-1, 58-2, . . . and 58-p to form a ground plane 64.

The read/write I/O solder bumps 48 are formed on top of the passivation layer 41. Traces 70-1, 70-2, . . . and 70-n that are formed on the passivation layer 41 provide a connection to corresponding interconnects defined by metal layers of the preamplifier IC 40. As can be appreciated, by forming the solder bumps 48 and providing traces on the passivation layer 41, post processing can be used to adapt the preamplifier IC 40 to flex circuits 10′ that are provided by different manufacturers. In other words, alignment variations can be adjusted using the traces 70 without requiring changes to the preamplifier IC 40 die.

Trace 74-1 connects the solder bump 52-1 to the second solder bump 52-2 (associated with the first voltage source V_(EE)) and/or to metal layers of the preamplifier chip 40. Trace 74-2 connects the solder bump 56-1 to the second solder bump 56-2 (associated with the second voltage source V_(DD)) and/or to the metal layers of the preamplifier chip 40 to power other circuits.

Referring now to FIGS. 3 and 4, a flex circuit 10′ according to the present invention includes first, second and third traces 100-1, 100-2 and 100-3. The first trace 100-1 provides a second ground shield between read/write channels and the power supply voltages V_(DD) and V_(EE). The second trace 100-2 distributes V_(EE) to the solder bumps 50 and the preamplifier circuits. The third trace 100-3 distributes V_(DD) to the solder bumps 54 and the preamplifier circuits. The flex circuit 10′ includes traces 104-1, 104-2, . . . , and 104-x that provide connections between the inductive elements 20 and the individual read and write circuits.

The flex circuit 10′ includes traces 108-1, 108-2, . . . 108-n that provide connections between read/write I/O of the connector 14 and the read/write bumps 48-1, 48-2, . . . and 48-n of the preamplifier circuit 40. The flex circuit 10′ includes traces 112, 114 and 116 that provide a connection between the voltage source inputs and ground of the connector 14 and the preamplifier circuit 40. The flex circuit 10′ includes a ground plane 120 that contacts the ground solder bumps 58-1. 58-2, . . . and 58-p and the traces 64. The ground plane 120 and ground plane 64 act as a heat sink to dissipate heat generated by the preamplifier.

More particularly, the first trace 100-1 is connected to ground solder bumps 60-1 and 60-2. The second trace 100-2 is connected to solder bumps 50 and 52. The third trace 100-3 is connected to solder bumps 54 and 56. The ground plane 120 is connected to solder bumps 58 and the traces 64.

Referring now to FIG. 5, a side cross-sectional view of the preamplifier circuit assembly including the preamplifier IC 40 and the flex circuit 10′ is shown. The preamplifier IC 40 includes a substrate 150 with active device layers 152. One or more interconnecting layers 154 are formed on the active device layers 152. One or more passivation layers 156 are formed on the interconnecting layers 154. Traces 158 (for example defining ground plane 64) are formed on the passivation layer 156. One or more insulating layer(s) 160 maybe formed over the traces 158. Solder bumps 162 and 164 provide a connection between the traces 34′ on the flex circuit 10′ and the interconnecting layers 154 when the preamplifier IC 40 is mounted or otherwise connected to the flex circuit 10′.

As can be appreciated, the first trace 100-1 provides a ground shield that surrounds the traces 100-2 and 100-3 to reduce noise from the voltage sources V_(EE) and V_(DD). The ground planes 64 and 120 provide heat dissipation. The flex circuit 10′ and the preamplifier IC 40 allow power and ground to be routed to every channel on the preamplifier chip 40 through traces on the single-layer flex circuit 10′. The distribution of power using the traces and the increased number of solder bumps reduces die temperatures of the preamplifier IC 40. The increased width of the traces on the passivation layer 41 have a reduce resistance (as compared with traces in the metal layers of the preamplifier IC), which reduces I²R losses. The present invention also reduces the complexity of interconnections that need to be made in the interconnecting layers of the preamplifier IC, which reduces cost.

Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims. 

What is claimed is:
 1. A preamplifier integrated circuit (IC) for a magnetic storage device, the preamplifier IC comprising: a plurality of channels, each including at least one preamplifier; a plurality of groups that each include at least one of the channels; at least one interconnecting layer; a passivation layer arranged adjacent to the at least one interconnecting layer; and a first solder bump arranged in a first opening in the passivation layer, the first solder bump to distribute a first potential to a first group of the plurality of groups but not to a second group of the plurality of groups; a second solder bump arranged in a second opening in the passivation layer, the second solder bump to distribute the first potential to the second group but not to the first group; and a flex circuit that includes a first trace, the first trace to distribute the first potential to the first solder bump and the second solder bump.
 2. The preamplifier IC of claim 1, further comprising a third solder bump arranged in a third opening in the passivation layer, the third solder bump to distribute the first potential to a third group of the plurality of groups but not to i) the first group and ii) the second group, wherein the first trace distributes the first potential to the third solder bump.
 3. The preamplifier IC of claim 1, further comprising: a third solder bump arranged in a third opening in the passivation layer, the third solder bump to distribute a second potential to the first group but not to the second group; and a fourth solder bump arranged in a fourth opening in the passivation layer, the fourth solder bump to distribute the second potential to the second group but not to the first group, wherein the flex circuit includes a second trace, the second trace to distribute the second potential to the third solder bump and the fourth solder bump.
 4. The preamplifier IC of claim 3, further comprising: a fifth solder bump arranged in a fifth opening in the passivation layer, the fifth solder bump to distribute a reference potential to the first group; and a sixth solder bump arranged in a sixth opening in the passivation layer, the sixth solder bump to distribute the reference potential to the second group, wherein the flex circuit includes a third trace, the third trace to distribute the reference potential to the fifth solder bump and the sixth solder bump.
 5. The preamplifier IC of claim 4, further comprising: ground shield solder bumps arranged on the flex circuit, the ground shield solder bumps connected to a ground shield trace, the ground shield trace being arranged radially outside each of the first solder bump, the second solder bump, the third solder bump, the fourth solder bump, the fifth solder bump, and the sixth solder bump.
 6. The preamplifier IC of claim 3, wherein the first solder bump and the second solder bump are arranged (i) radially inside each of the third solder bump and the fourth solder bump or (ii) radially outside each of the third solder bump and the fourth solder bump.
 7. The preamplifier IC of claim 3, wherein the first trace does not overlap the second trace.
 8. The preamplifier IC of claim 3, further comprising an insulating layer arranged adjacent to the first trace.
 9. The preamplifier IC of claim 1, wherein the flex circuit includes a substrate and the first trace is formed on the substrate.
 10. The preamplifier IC of claim 1, further comprising: a third solder bump arranged in a third opening in the passivation layer, the third solder bump to distribute the first potential to the first solder bump and the second solder bump via the first trace. 